From prior art it is known, for instance, how to operate an oil pump directly from an engine shaft or a coupling therefrom. In special circumstances the need of liquid might, however, be larger than the normal capacity of the used pump. As a remedy for that a hand-operated pump was previously introduced giving extra liquid for each pump stroke the operator made. A separate hand-operated pump must be placed easily accessible and have its own connections from the tank to the position of supply. A simplification of the problem has been possible by introducing a control member for the capacity of the pump which is easily checked by the operator during operation, and such a member is utilized in the present invention.